Recently, size reduction of a power conversion device is required, so it is important to reduce the size of a power semiconductor module used therein.
As a general structure of a power semiconductor module, a wiring pattern is formed via an insulating layer on a metal plate serving as a heat dissipating plate, a power semiconductor element is provided thereon and connected with each terminal by a wire bond, and then these are sealed with resin.
Such power semiconductor modules can be roughly classified into two types, i.e., a case-type module which is sealed with silicone gel and a transfer-mold-type module which is sealed with epoxy resin (for example, see Patent Document 1 for the former one and Patent Document 2 for the latter one). The former case-type module often uses a ceramic insulating layer as the insulating layer, and the latter transfer-mold-type module often uses a resin insulating layer.
In a power semiconductor module that performs switching operation with large current and high voltage, a temporal change rate di/dt of current when a power semiconductor element is turned off and a wiring inductance L contained in a power conversion device cause surge voltage ΔV=L·di/dt to be applied to the power semiconductor element. If the wiring inductance L is great, surge voltage that exceeds withstand voltage of the power semiconductor element occurs, which may cause deterioration in the power semiconductor element.
Therefore, for a power semiconductor module, size reduction is required, and also reduction of inductance is important.
For example, in a conventional semiconductor module, a semiconductor element as an electronic component is mounted on a ceramic circuit board including a ceramic multilayer board formed by three or more laminated ceramic boards bonded with each other, surface-layer metallic circuit boards bonded on the upper surface and the lower surface of the ceramic multilayer board, an inside-layer metallic circuit board placed in a circuit through hole formed in inside-layer ceramic boards, and a metallic pole having one end connected to an inside-layer metallic circuit board and the other end connected to another inside-layer metallic circuit board or a surface-layer metallic circuit board with a brazing material so that the inside-layer metallic circuit board is connected with the other inside-layer metallic circuit board or the surface-layer metallic circuit board (for example, see Patent Document 3).
In addition, for example, in a conventional semiconductor module, a bus bar inside the module is formed in a lamination structure so as to reduce an inductance at the bus bar portion, thereby realizing inductance reduction of the semiconductor module (for example, see Patent Document 4).